Here's why:

* Wood: The wooden body of a pencil is a good insulator. Wood doesn't allow electricity to flow through it easily.

* Graphite: The graphite core of a pencil is a conductor, but it's a poor conductor. While it can carry a small amount of electricity, it's not nearly as conductive as metals like copper or silver.

The graphite core is only a conductor because of its structure:

* Layered Structure: Graphite is made of layers of carbon atoms bonded in a hexagonal pattern. The electrons in these layers can move freely, allowing for some electrical conductivity.

* Weak Interlayer Bonding: The layers are held together by weak forces, allowing them to slide past each other. This makes graphite a good lubricant and also contributes to its ability to leave a mark on paper.

In summary: While a pencil's graphite core has some conductive properties, the overall structure of the pencil (with the wood body) makes it act as an insulator.